In general, a power supply system, which supplies power to various loads placed on a floor surface, is either of the followings in a broad sense: a contact-type power supply system configured to supply power by bringing electrodes, which are provided in a manner exposed over the floor surface, into direct contact with electrodes provided on the bottom surface of a load; and a contactless power supply system configured to supply power without bringing electrodes, which are provided in an unexposed state underneath a floor surface, into direct contact with electrodes of a load.
Patent Document 1, for example, discloses a conventional one of such contactless power supply systems. This system supplies power to a load (aboveground movable body) that moves along a guideway. The system is configured in such a manner that, while an induction line is arranged along the guideway, an iron core wounded with a coil is provided to the aboveground movable body. Then, power is supplied to the aboveground movable body when electromagnetic induction, with the induction line being the primary side and the coil being the secondary side, is generated when a high-frequency current is flown through the induction line.
Non-patent Document 1 also discloses a wireless power transmission sheet as another contactless power supply system. This wireless power transmission sheet is configured in such a manner that power-transmitting coils, an MEMS (Micro Electro Mechanical Systems) switch used for controlling power, a position detection coil used for detecting the position of a power-receiving device, and an organic transistor to perform position detection by using the position detection coil are formed on a plastic film by use of printing techniques. This wireless power transmission sheet uses the organic transistor to detect a change in inductance of the position detection coil, thereby identifying the position of an electronic device that has approached, the change accompanying the approach of the electronic device to the sheet. Further, the wireless power transmission sheet selects one of the power-transmitting coils by using the MEMS switch, and transmits power through the thus selected power-transmitting coil, the one corresponding to the thus identified position.
In order to obtain higher power transmission efficiency, however, the conventional contactless power supply system as described above requires a lot of positional restrictions including the need for closely positioning an induction line and a coil, and the need for aligning these induction line and coil with each other so that a magnetic flux generated by electrical conduction through the induction line may pass through the central axis of the coil. Therefore, there has been a problem that, since power supply has been possible only on a fixed route such as a guideway, power supply to a movable body such as a robot that needs to freely move on a floor surface has been impossible. Further, a magnetic body such as an iron core should be used in forming a magnetic path, which raises another problem that the system is made heavy, and produces noise due to magnetostriction generated in altering-current energization of the magnetic body. On the other hand, the conventional wireless power transmission sheet also has a lot of positional restrictions for the purpose of achieving higher power transmission efficiency, the restrictions including the need for aligning the positions of the power-transmitting coil and a power-receiving coil of the electronic device with each other. Further, the conventional wireless power transmission sheet employs a lot of switches, and therefore, there is a possibility of reliability degradation. Although another possible type of contactless power supply system is one that supplies power through electromagnetic waves, the use of electromagnetic waves is strictly regulated so that danger to human bodies and malfunctions of electronic devices may be avoided. Installation of this type of contactless power supply system has been therefore difficult to be installed in a place to have people inside, such as an office space.
In consideration of the above described issues, the present applicants proposed a power supply system that uses neither electromagnetic induction nor electromagnetic waves, and is still capable of contactless power supply by using series resonance (refer to Patent Document 2 but note that, as of the filing date of the present application, the power supply system thereof was not publicly known as Patent Document 2 had not been disclosed). The summary of this power supply system will be described below.
FIG. 11 shows a vertical cross-sectional view of essential parts of the conventional power supply system as described above. This power supply system is a power supply system for supplying power, via a movable body 103 arranged in a power-consuming region 102, to a load 104 from a fixed body 101 placed in a power-supplying region 100. The fixed body 101 includes a first power-transmitting electrode 105 and a second power-transmitting electrode 106, which are arranged at positions in the neighborhoods of the interface between the power-supplying region 100 and the power-consuming region 102. The movable body 103 is supposed to be placed at a position in the neighborhood of the interface, and includes a first power-receiving electrode 107 and a second power-receiving electrode 108, which are placed in a manner opposed to and not contacting the first power-transmitting electrode 105 or the second power-transmitting electrode 106. The first and second power-transmitting electrodes 105 and 106 and the first and second power-receiving electrodes 107 and 108, in combination, form coupling capacitors 109. Each of these coupling capacitors 109 in combination with a coil 110 forms a series resonance circuit. This configuration enables highly efficient power supply from the fixed body 101 to the movable body 103. Specifically, this configuration makes the following case possible. With a large number of the fixed bodies 101 each as described above being arranged side by side under a floor board 111, power is continuously supplied to the movable body 103 in a contactless manner at the same time as the movable body 103 is caused to travel and move on this floor board 111.
In this power supply system, an AC power supply 115, the frequency of which is controllable by switching, is provided to the fixed body 101. This AC power supply 115 supplies AC power to the first power-transmitting electrode 105 and second power-transmitting electrode 106, the AC power having a desired frequency.
Additionally, for the purpose of performing power supply control, this power supply system is configured to have the function of enabling communication between the fixed body 101 and movable body 103. Specifically, a communication unit 112 is provided to each of the fixed bodies 101, and a communication unit 113 is provided to the movable body 103. A power supply request signal is transmitted from the communication unit 113 of the movable body 103. Each of the fixed bodies 101, upon receiving the power supply request signal through the communication unit 112 thereof, deems the movable body 103 to be located above itself and perform power supply control.
Nevertheless, even though the fixed body 101 is enabled to determine whether the movable body 103 is located above itself, this does not necessarily allow determination, when the movable body 103 moves in random direction, as to which of the first power-receiving electrodes 107 and second power-receiving electrodes 108 is an electrode placed in a manner opposed to the first power-transmitting electrode 105, and as to which of the first power-receiving electrodes 107 and second power-receiving electrodes 108 is an electrode placed in a manner opposed to the second power-transmitting electrode 106. To make this determination possible, a connection section 114 having multiple diodes is used for rectification, whereby continuous power supply is enabled in a manner suited for the polarity of the load 104 regardless of how each of the electrodes is opposed to another one thereof. With the diodes being thus arranged in the movable body 103, provision of the coil 110 between the diodes and the load 104 would make it impossible to cause series resonance between the coil 110 and the coupling capacitor 109 because the diodes would rectify currents. In order to avoid this situation, the coil 110 is arranged in the fixed body 101 side.
This power supply system eliminates the need for exposing the first and second power-transmitting electrodes 105 and 106 to the power-consuming region 102, which facilitates installation thereof in a place to have people inside. Further, this power supply system is capable of supplying power as long as each of the electrodes is placed in a manner opposed to another one thereof with a distance therebetween which makes these electrodes close enough to produce a desired capacitor capacity therebetween. This capability eliminates the need for strict alignment as has been done in the case of a power supply system using electromagnetic induction, and therefore enables power supply to the movable body 103 even in a case where the movable body 103 is a robot.